2 groups with the same answer?! As well as others that could fit in those groups. Marked low for that

"2 groups with the same answer?!"

There are no two groups with the same answer.

"As well as others that could fit in those groups."

Those are red herrings. While multiple answers fit into one group, there is only one combination of answers that allow you to have four answers that fit each distinct description for each group. So you can have six possible answers in Group A, but only one of those six also fit in Group B and only one of them fits in Group C. You have to identify those that belong in other groups before you can complete Group A.

Allow me to explain myself and if I did something wrong, I'll happily stand corrected. I am just not convinced, at least not yet, that I did something wrong.

There are six correct answers for the A group.
Five correct answers for the B group.
Four correct answers for the C group.
Five correct answers for the D group.

Once the four correct answers for the C group, the only possible solution, is removed, there are only four correct answers left for the D group.

Once the four remaining correct answers for the D group, the only remaining possible solution, is removed, there are only four correct answers left for the B group.

Once the four remaining correct answers for the B group, the only remaining possible solution, is removed, there are only four answers left for the A group and they happen to be the correct ones.

If I have done something wrong, I do want to know about it, but from your reply I simply don't understand what i have done wrong. If I understand it correctly the key is that there is only one correct solution where all sixteen answers are solved into four categories and, as long as that is so, you can have as many answers you like that fit into one category.

I'd be happy to listen and learn.

Personally the lack of subject matter diversity is more of an issue here than technicality of grid construction but I appreciate any effort to entertain the puzzling masses.

I think that this is an absolutely fine grid. Thanks, I enjoyed it.